Method of manufacturing an electrical capacitor

ABSTRACT

A power factor correction capacitor is constructed of several capacitor packs, each having convolutely wound layers of aluminum foil and polypropylene film with two layers of polypropylene film between the layers of foil. The several capacitor packs are assembled into a case and impregnated with trichlorodiphenyl with a bis (3, 4-epoxy-6-methylcyclohexylmethyl) adipate as an additive. During the winding process the foil is deformed by a deforming roller rolled against the roll of foil as it is wound into the capacitor pack.

United States Patent [191 Lapp et al,

[111 3,831,234 Aug. 27, 1974 METHOD OF MANUFACTURING AN ELECTRICALCAPACITOR [75] Inventors: John Lapp, Franklin; Norbert R.

Weiler, Greendale, both of Wis.

[73] Assignee: McGraw-Edison Company, Elgin,

Ill.

22 Filed: Apr. 6, 1973 211 App]. No.: 348,656

Related U.S. Application Data [62] Division of Ser. No. 255,156, March10, 1972, Pat.

[52] U.S. Cl. 29/2S.42, 242/561, 317/260 [51] Int. Cl H013 13/00 [58]Field of Search 317/258, 259, 260;

[56] References Cited UNITED STATES PATENTS 1,770,851 7/1930 Hayman174/25 R 3,027,628 4/1962 Wilk et a1.

2/1969 Johnstone 317/260 X 3,432,901 3/1969 Fanning 29/25.42

3,450,968 6/1969 Cox 317/258 3,588,644 6/1971 Nash et all 317/259FOREIGN PATENTS OR APPLICATIONS 106,535 2/1939 Australia 317/260 PrimaryExaminer--Charles -W. Lanham Assistant ExaminerCarl E. Hall [57]ABSTRACT A power factor correction capacitor is constructed of severalcapacitor packs, each having convolutely wound layers of aluminum foiland polypropylene film with two layers of polypropylene film between thelayers of foil. The several capacitor packs are assembled into a caseand impregnated with trichlorodiphenyl with a his (3,4-epoxy-6-methylcyclohexylmethyl) adipate as an additive. During thewinding process the foil is deformed by a deforming roller rolledagainst the roll of foil as it is wound into the capacitor pack.

26 Clains, l3 Ih'awing Figures PAIENIEnmczmw SHEET 10F 2 I FIG. 3

PAIENTEDwszmu SHEEI 2 OF 2 FIG. 10

FIG. 11

.METHOD QF MANUFACTURING AN ELECTRICAL CAPACITOR standard practice touse aluminum. foil as the electrode and to use twolayers ofpolypropylenefilm separated by paperas the dielectric materialbetweenthe layers of foil with a chlorinated diphenyl and asuitablestabiliz ing additive as an irnpregnant lnthe development of pacitor wasan improvement over the older all-paper capacitors which usedonly-paperbetween the foils. The paper-film capacitor, as compared tothe all-paper capacitor, has about one-third thelosses, 30% greaterenergy density, and increased reliability. Also, the paper has a loweraverage voltage stress resulting in a lower energy density, However, thepaperproduces a significant amountof dielectricloss. Therefore, it hasbeen apparent that elimination of the paper couldproduce a superiorcapacitor. However, after much experimentation and developmnt work, thecreation of a fully satisfactory all-filmcapacitor has not beenpreviously achieved.

With this invention a low cost all-film capacitor that is highlyreliable and efficient and, in fact, has all the desirablecharacteristics of and is in many ways superior to the paper-filmcapacitor is provided. This is accomplished primarily by modification ofthe manufacturing techniques and by selectively deforming the foil in amanner that enables substantially complete impregnation of the film bythe chlorinated diphenyl.

Objects and advantages of the invention will be apparent from thefollowing detailed description.

FIG. 1 is a perspective view of a capacitor packconstructed according tothis invention;

FIG. 2 is a perspective view of a power capacitor having severalcapacitor packs, as shown in FIG. 1, connected in series;

FIG. 3 is a simplified schematic drawing of a capacitor winding machineused to wind the capacitor pack shown in FIG. 1;

FIG. 4 is a simplified perspective view of a portion of the windingmachine shown in FIG. 3 showing the deforming roller and foil roll inmore detail;

FIGS. 5A, 5B and 5C are end views of foil sections illustrating threeexemplary types of deformations of the foil that occur; v

FIG. 6 is a top view of a foil section of foil having exemplarydeformations as in FIG. 5;

FIGS. 7, 8 and 9 are partial sectional end views of a capacitor packshowing difierent configurations of lapping of the foil and film;

FIG. 10 is a more detailed showing of the roller shown in FIG. 4; and

FIG. 11 is a partial detailed view of the deforming roller shown in FIG.10.

Referring. to FIG. 1, a capacitor pack 10 comprises film strips 11 and12 of any suitable dielectric polymeric film forming a first film layer,film strips 13 .and 14 forming a second film layer, and foil strips 17and 18 of any suitable conductive material between the film layersconvolutely wound and compressed to form a flattened pack as shown. Filmstrips 13 and 14 are .wound between foil 18 and foil 17 of the nextlayer of film and foil, and strips 11 and 12 are wound between foilstrips 17 and 18, all continuously wound to produce a capacitor packhaving two plates or electrodes formed by foilstrips -l7 and 18,respectively. Electrical conneC.ting tabs 21 and 22 are inserted to makean electrical connection to foil strip 17 and foil strip 18, re-

spectively, in a manner known in the art.

Referring to FIG. 2, a power capacitor 24 comprises a casing 25, severalcapacitor packs 10 connected in series or as desired to provide adesired characteristic for the capacitor, and electrical terminals 26and 27 capacitors the paperrpolypropylene, or papenfilrn, ca-

mounted within insulating bushings 28 and 29, respectively, which aremounted in openings in casing 25. The

. capacitor uses any suitable metallic foil, such as aluminum foil, asthe conductive foil and is impregnated with atsuitable dielectricorganic liquid, typically a halogenated aromatic compound such as, forexample, trichlorodiphenyl. For best results a suitable stabilizingadditive is added to the dielectric liquid and may be, for example, anysuitable epoxide, such as bis (3, 4-epoxy- -methylcyclohexylmethyl)adipate. The dielectric film is a suitable dielectric polymericcompound, such as, for example, polypropylene.

Referring to. FIG. 3, a capacitor winding machine 30,

generally of any known type that may be used to wind a capacitor pack,such as capacitor pack 10, is shown ina simplified form and comprises awinding means for winding film strips 11, 12, 13 and 14 and foil strips17 and 18 into a capacitor pack; a film holding means for holding andunwinding rolls, of film; a foil holding means-for holding and unwindingrolls of foil; a control means for controlling the winding means, thefilm holding means, and the foil holding means to effect the un rollingof rolls of film and foil and the winding onto the winding means to formthe capacitor pack; and a deforming means for deforming the foil byapplying a selected pressure at selectively positioned points to theroll of foil as it is being unwound to produce selected deformationthrough several layers of foil on the roll.

The winding means comprises a winding spindle or roller 32 mounted on apanel 33 and rotatable by any known means (not shown) in a clockwisedirection (as seen in FIG. 3) to roll the foil strips and film stripsinto capacitor pack 10.

The film holding means comprises idler rollers 3411, 34b, 34c and 34d,film spindles or rollers 35, 36, 37 and 38, each adapted in any knownmanner to hold and unwind film rolls 41, 42, 43 and 44, respectively, bybeing controllably rotated in a counterclockwise direction by any knownmeans (not shown).

The foil holding means comprises idler rollers 45a,

45b, 45c and 45d; spindles or rollers 46 and 47 adapted 37 and 38 andfoil rollers 46 and 47 to assure a tight uniform capacitor pack in anymanner known in the art. This may be done by controlling and correlatingthe rotation of the rollers or by placing appropriate controlled tensionon the rollers to insure a tight roll and to insure that breaking doesnot occur as the film and foil are wound into a capacitor pack.

The deforming means comprises a deforming roller assembly 50 and asimilar deforming roller assembly 51 each adjacent foil rolls 48 and 49,respectively, to deform the foil on each foil roll. Referring to FIG. 4,de forming roller assembly 50 is shown in a simplified and schematicform, is mounted on panel 33, and comprises a support block 52'mountedon panel 33 in any known manner adjacent to foil roll 48 and foil roller46, a deforming roller 53, a roller support frame 54 passing throughguide holes 55 and 56 in support block 52 and supporting deformingroller 53, and a biasing means ineluding a spring 57 connected betweensupport frame 54 and support block 52 to apply compressive force betweendeforming roller 53 and foil roll 48. The biasing means may be of anyknown type that can apply a controlled and even force to force roller 53against foil roll 48. The roller assemblies thus include a means forforcing the deforming rollers to press against foil rolls 48 and 49 witha selected force furnished by some appropriate means such as spring 57so that some degree of deformation takes place through several layers offoil.

Referring to FIGS. 10 and 11, deforming roller 53 is shown in aschematic detail and has spirally cut pyramidal shaped points 61resulting from oppositely spiraling grooves 62 and 63 and preferably hasthe points positioned about fourteen to the inch across the roller. Thisconfiguration has been shown to provide satisfactory deformation of thefoil with a reasonable pressure, in the range of 1500 grams/linear inchof contact, which will result in satisfactory impregnation of thecapacitor rolls when assembled.

Referring to FIGS. A, 5B and 5C exemplary foil strip sections 65, 66 and67 have deformations resulting from deforming roller 53. Thedeformations can be categorized to be said to take any one of the threeforms 65A, 66A or 67A on foil sections 65, 66 and 67, respectively.Deformations 65A conform to the configuration of points 61 of deformingroller 53, deformations 66A have blunted edges and take a truncatedpyramidal form, and deformations 67A are perforations caused as points61 force through the foil. The perforation holes are small, with amaximum size of about pinhole size, and just barely visible to the nakedeye when viewed against a bright light behind the foil. Having abouttwenty per cent of the indentations perforated seems to be a goodportion to insure proper impregnation although the range can apparentlybe quite great, perhaps up to about fifty per cent or more. The foil hasa combination in a random manner of the three different types ofdeformations and of the variations of each type to produce an exemplaryfoil strip section 68 as shown in FIG. 6. The deformations are acombination of the three deformations shown in FIG. 5 in combinationwith lesser deformations and indentations caused by the effect of thepoints through several layers of foil as pressed upon by the deformingroller. The maximum depth of deformation allowable appears to be abouteight mils, but a maximum depth of about six mils seems to be best.Contrary to usual expectations the deformations do not take up extraspace in the capacitor if generally within these tolerances.

FIG. 6 shows an' idealized, theoretical deformation that would occur inthese rows, A, B and C, through three layers. Actually, there isoverlapping of these deformations and there is some effect through aboutthirty to fifty layers when applied to foil of about 0.22 mils inthickness, a size of foil that has been shown to be highly satisfactory.A spacing between the rows of about one-fourteenth of an inch has beenfound to be satisfactory to accomplish this with a deforming rollerhaving pyramidal points extending upwardly by about 0.039 inches abovethe base of the grooves, as shown in FIG. 11. The first row A showstypical indentations placed on the outer layer with some fulldepressions F, some smaller depressions S, and some depressions Pproducing perforations. The second row B shows something that can occurat the second layer with a few full depressions F, a few partialdepressions S, and a few perforations P, and the third row C shows theeffect at the third layer where perforations are not likely to occur andthe depressions are not as deep or as sharply formed. The randomcombination and variations of these through the several layers combineto superimpose the deformations on top of each other in a random manneralong the rolls as the foil is unwound. If considered necessary, twodeforming rollers could be used for each roll of foil to insure a randompattern.

Referring to FIGS. 7, 8 and 9, since it is apparently easier to wet withthe liquid dielectric along the foilfilm layers than it is between filmlayers, it may be desirable to have at least one foil strip, such asfoil strip 17, as shown in FIG. 8, or both foil strips 17 and 18, asshown in FIG. 9, extend outwardly from the capacitor pack. However, allthe configurations shown in FIGS. 7, 8 and 9 appear to be satisfactory.

An all-film capacitor constructed according to this invention has beenfound to provide excellent characteristics. One of the characteristicsstudied is the corona starting voltage of several samples using twosheets of one-half mil polypropylene film with the film extended beyondthe deformed foil as shown in FIG. 7. It was found that the coronastarting voltages were very consistent over many series of tests andafter many hours of operation had remained in the range of 2600 to 3250volts. This has been found true even though the usual expectation ofthose skilled in the art was that deformations would be harmful becauseof increased electrical stresses at the deformation. The tests conductedon units according to this invention indicate that this is not true, andthe units were found to be superior to filmpaper capacitors.

Another advantage of this invention occurs in the method of constructionof capacitors in that complete impregnation of the dielectric into thecapacitor has been obtained without a previously required heatingprocess. Previously, capacitor manufacturing required heating thecapacitor pack to a temperature of 180 F or higher and applying a highvacuum to draw off any volatile material, such as water vapor, from thecapacitor pack. After the capacitor pack had been sufficiently dried, itwas cooled and an impregnant was added to impregnate the dielectricmaterial. The capacitor pack was then typically permitted to remainunder vacuum with the temperature above F but lower than about F. Thecapacitor was then sealed and ready for the manufacturing processes.

A capacitor constructed according to this invention eliminates a largeamount of the moisture present in the capacitor because of the absenceof paper since the film and foil do not substantially retain much watervapor and gas. Therefore, the small amount of moisture removal necessarycan be accomplished at room temperature or at only a slightly elevatedtemperature of about 80 or 90 F. This results in a shorter drying time,and no cooling of the unit is required before liquid is admitted forimpregnation purposes, thereby substantially reducing the totalprocessing time required.

Therefore, according to this invention a method of constructingcapacitors comprises winding a capacitor pack with convolutely woundalternate layers of film and foil with two layers of film between eachlayer of foil, deforming the foil by using a deforming roller of thetype shown pressing with a selected pressure against the roll of 'foilas it is being wound onto the capacitor roll. The pressure is selectedto produce indentations of the type desired-within a selected range ofdepths and selected percentage of perforations. After the capacitor rollis wound, it is then shaped into the desired shape and placed into astandard capacitor casing. The capacitor is then put under vacuum atroom temperature or a slightly raised temperature, and then issubsequently impregnated with a dielectric liquid such as chlorinateddiphenyl. The capacitor is then sealed and prepared for furthermanufacturing processes.

We claim: 1. A method of manufacturing a power capacitor comprising:

winding strips of conductive foil and dielectric film in alternatelayers into a capacitor pack by rolling at least two strips ofconductive foil and two strips of dielectric film off respective rollsof conductive foil and dielectric film; deforming at least one strip ofthe foil being wound by applying a deforming roller having selectivelypositioned raised points against the roll of foil with a force selectedto create some deformation of the foil at each of said points throughseveral layers of foil; placing the capacitor pack in a capacitorcasing; and

impregnating the capacitor pack with a dielectric liquid.

2. A method according to claim 1 wherein said step of impregnatingcomprises impregnating with a dielectric liquid having a stabilizingadditive.

3. A method according to claim 2 wherein said step of impregnatingcomprises impregnating with a halogenated aromatic liquid having anepoxide additive.

4. A method according to claim 3 wherein said aromatic compound is achlorinated diphenyl.

5. A method according to claim 1 also comprising placing the capacitorpack under vacuum prior to the step of impregnating.

6. A method according to claim 5 also comprising placing the capacitorpack at a temperature of about 8090 F for a selected period of timeafter placing said capacitor pack under vacuum.

7. A method according to claim 6 wherein said force is selected toproduce a random range of depth of deformations with some deformationscreating perforations.

8. A method according to claim 1 wherein said step of deformingcomprises deforming both strips of foil.

9. A method according to claim 8 wherein said force is selected toproduce a random range of depth of deformations with some deformationscreating perforations.

10. A method according to claim 9 wherein said force is selected toproduce a perforation range of about twenty per cent of thedeformations.

11. A method according to claim 10 wherein said deformations are ofvarying depth up to a maximum of about the magnitude of six mils.

12. A method according to claim 11 wherein said raised points arepositioned to produce rows of indentations having random depths ofindentations and a random percentage of perforation.

13. A method according to claim 12 wherein said step of deformingcomprises creating perforations in about twenty to fifty per cent of theindentations.

' 14. A method according to claim 12 also comprising placing thecapacitor pack under vacuum prior to the step of impregnating. v

15. A method according to claim 14 also comprising placing the capacitorpack at a temperature of about F for a selected period of time afterplacing the capacitor pack under vacuum.

16. A method according to claim 15 wherein said step of deformingcomprises applying a deforming roller having points positioned on saidroller to produce rows of indentations spaced apart by aboutonefourteenth of an inch.

17. A method according to claim 8 also comprising placing the capacitorpack under vacuum prior to the step of impregnating.

18. A method according to claim 17 also comprising placing the capacitorpack at a temperature of about 8090 F prior to the step of impregnating.

19. A method according to claim 18 wherein said deformations are ofvarying depth up to a maximum of about the magnitude of six mils.

20. A method according to claim 19 wherein said step of deformingcomprises creating perforations in about twenty per cent of theindentations.

21. A method according to claim 20 wherein said raised points arepositioned and said force selected to produce rows of indentationshaving randomly determined depths of indentations within a selectedrange of depth and with a selected percentage of perforation.

22. A method according to claim 2 also comprising placing the capacitorpack under vacuum prior to the step of impregnating.

23. A method according to claim 22 also comprising placing the capacitorpack at a temperature of about 80'90 F prior to the step ofimpregnating.

24. A method according to claim 8 wherein said raised points arepositioned and said force selected to produce rows of indentationshaving randomly determined depths of indentations within a selectedrange of depth and with a selected percentage of perforation.

25. A method according to claim 24 also comprising placing the capacitorpack under vacuum prior to the step of impregnating.

26. A method according to claim 25 also comprising placing the capacitorpack at a temperature of about 80-90 F following the step of placingunder vacuum and prior to the step of impregnating.

2. A method according to claim 1 wherein said step of impregnatingcomprises impregnating with a dielectric liquid having a stabilizingadditive.
 3. A method according to claim 2 wherein said step ofimpregnating comprises impregnating with a halogenated aromatic liquidhaving an epoxide additive.
 4. A method according to claim 3 whereinsaid aromatic compound is a chlorinated diphenyl.
 5. A method accordingto claim 1 also comprising placing the capacitor pack under vacuum priorto the step of impregnating.
 6. A method according to claim 5 alsocomprising placing the capacitor pack at a temperature of about 80*-90*F for a selected period of time after placing said capacitor pack undervacuum.
 7. A method according to claim 6 wherein said force is selectedto produce a random range of depth of deformations with somedeformations creating perforations.
 8. A method according to claim 1wherein said step of deforming comprises deforming both strips of foil.9. A method according to claim 8 wherein said force is selected toproduce a random range of depth of deformations with some deformationscreating perforations.
 10. A method according to claim 9 wherein saidforce is selected to produce a perforation range of about twenty percent of the deformations.
 11. A method according to claim 10 whereinsaid deformations are of varying depth up to a maximum of about themagnitude of six mils.
 12. A method according to claim 11 wherein saidraised points are positioned to produce rows of indentations havingrandom depths of indentations and a random percentage of perforation.13. A method according to claim 12 wherein said step of deformingcomprises creating perforations in about twenty to fifty per cent of theindentations.
 14. A method according to claim 12 also comprising placingthe capacitor pack under vacuum prior to the step of impregnating.
 15. Amethod according to claim 14 also comprising placing the capacitor packat a temperature of about 80*-90* F for a selected period of time afterplacing the capacitor pack under vacuum.
 16. A method according to claim15 wherein said step of deforming comprises applying a deforming rollerhaving points positioned on said roller to produce rows of indentationsspaced apart by about one-fourteenth of an inch.
 17. A method accordingto claim 8 also comprising placing the capacitor pack under vacuum priorto the step of impregnating.
 18. A method according to claim 17 alsocomprising placing the capacitor pack at a temperature of about 80*-90*F prior to the step of impregnating.
 19. A Method according to claim 18wherein said deformations are of varying depth up to a maximum of aboutthe magnitude of six mils.
 20. A method according to claim 19 whereinsaid step of deforming comprises creating perforations in about twentyper cent of the indentations.
 21. A method according to claim 20 whereinsaid raised points are positioned and said force selected to producerows of indentations having randomly determined depths of indentationswithin a selected range of depth and with a selected percentage ofperforation.
 22. A method according to claim 2 also comprising placingthe capacitor pack under vacuum prior to the step of impregnating.
 23. Amethod according to claim 22 also comprising placing the capacitor packat a temperature of about 80*-90* F prior to the step of impregnating.24. A method according to claim 8 wherein said raised points arepositioned and said force selected to produce rows of indentationshaving randomly determined depths of indentations within a selectedrange of depth and with a selected percentage of perforation.
 25. Amethod according to claim 24 also comprising placing the capacitor packunder vacuum prior to the step of impregnating.
 26. A method accordingto claim 25 also comprising placing the capacitor pack at a temperatureof about 80*-90* F following the step of placing under vacuum and priorto the step of impregnating.